In recent years, due to the technical advancement of image sensing apparatuses using CCDs and other solid-state image sensors, as well as higher capacities and lower prices of semiconductor memory cards, digital video cameras with still image shooting capabilities and digital still cameras with movie shooting capabilities have become commonplace.
Furthermore, some image sensing apparatuses recently introduced to the market are not only capable of choosing between a movie shooting mode and a still image shooting mode to shoot either movies or still images under a chosen mode, but also capable of shooting still images during movie shooting without having to switch modes.
However, since movie shooting generally requires processing speeds of 30 frames per second, and individual frame images are not envisioned to be viewed as still images, movie shooting is generally performed using a resolution lower than that used for still image shooting. Also, auto focus control put a priority on a focus tracking ability, e.g., for a moving subject, over focus accuracy.
Therefore, in the case of shooting still images during movie shooting, applying the same auto focus control as during movie shooting is likely to result in images not well focused. Thus, it is preferable to perform an auto focus control for still image shooting.
When processing still image shooting during movie shooting, it is difficult to perform the two processes in a completely parallel manner. In reality, movie recording will be interrupted. Therefore, proposals have been made to minimize the interruption period of movie recording caused by the still image shooting process, or to suppress the unnaturalness of playback by generating images for the interruption period from other frames.
For instance, Japanese Patent Laid-Open No. 2004-201282 proposes a method for reducing the interruption period of movie recording. To be more precise, a method is described where movie recording will be continued until a shutter button for still image shooting is fully pressed, even in the event that the shutter button is pressed halfway to perform auto focus control or automatic exposure control.
According to the method proposed in this literature, since movie recording is not interrupted until shooting actually occurs, the interruption period of movie recording can be reduced as compared to a case where pressing the shutter button halfway immediately interrupts movie recording. Even so, a problem remains where auto focus (AF) control or automatic exposure (AE) control for still image shooting performed upon halfway pressing of the shutter button affects the movie that is being continuously recorded.
In other words, AF control during still image shooting typically involves performing full-range scans between a near end and a far end with a focus lens to determine a focus position. This means that images obtained while driving the focus lens during the AF control will be included in the movie being continuously recorded. Therefore, when a photographer determines a desired shooting position or range by repeatedly halfway-pressing and releasing the shutter button, an out of focus moving image will be recorded every time the shutter button is pressed halfway. Thus, there was a problem where movie playback was visually undesirable.